This invention relates to power cylinders operated by hydraulic pressure and more particularly to a hydraulic pressure power cylinder including means to securely lock the piston in a desired position of the piston.
Power cylinders find many applications in modern industry. For example, power cylinders are utilized to advance the slide of a tool head in a machine tool so as to bring the cutting tool to a position to operate on a workpiece. If the piston is not locked in this position of adjustment, the associated tool may bounce back and forth or chatter when it is moved against and into the work. As a further example, power cylinders are also conventionally used to operate work holding clamps. It is essential in each situation that the cylinder hold the workpiece securely and that it maintain a holding force on the work, sometimes for long periods of time and sometimes regardless of variations in the size of the work due to permissible work tolerances or other factors. It is important that the power clamps used to hold parts maintain full pressure continuously and that pressure not be relieved or even reduce appreciably at any clamp during the entire period.
It is important therefore, in these and other applications, that the power cylinder include means to ensure that the piston and thereby the associated tool or clamp maintains its position of adjustment irrespective of forces exerted against the associated tool or clamp and irrespective of pressure losses in the cylinder.
Various devices have been proposed to allow the piston to be locked in a particular position of adjustment. Whereas these prior art locking devices have been generally acceptable, they suffer from several disadvantages. Specifically, they are often able to provide locking of the piston only at particular points in the stroke of the piston and they typically have a complex structure and operation resulting in a high initial manufacturing cost and further resulting in high maintenance costs.